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What is Subaortic Stenosis?

Subaortic stenosis is an obstruction or narrowing at the outlet of the lower left chamber of the heart (the left ventricle), just below the aortic valve. In typical subaortic stenosis, the aortic valve itself is normal.

The normal heart has four chambers: two upper chambers called atria, which receive blood into the heart, and two lower chambers called ventricles, which pump blood out of the heart. Ordinarily, unoxygenated (blue) blood comes back from the body into the right atrium, moves into the right ventricle, and then is pumped out of the right ventricle through the pulmonary artery (the main artery to the lungs) to collect more oxygen. The now-oxygenated (red) blood returns from the lungs and enters the left atrium, moves into the left ventricle, and then is pumped through the left ventricle's outflow tract to the aortic valve and out to the body through the aorta (the body’s main artery).

In a heart with subaortic stenosis, it is difficult for the left ventricle to pump the blood to the body due to the narrowed area in the outflow tract below the aortic valve.

Subaortic stenosis can cause two main problems for the heart:

  • The blockage can cause extra work for the left ventricle.
  • Turbulent blood flow created by the narrowing may damage the aortic valve, causing an otherwise normal valve to leak. This is called aortic valve insufficiency.

There are two kinds of subaortic stenosis:

  • Discreet subaortic stenosis, the more common form, occurs when a membrane composed of fibrous tissue forms an obstruction beneath the aortic valve.
  • Tunnel subaortic stenosis, a less common and more complex form, occurs when the pathway between the ventricle and valve is narrow for the entire distance.

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What are the causes?

The causes of heart defects such as subaortic stenosis among most babies are unknown. Some babies have heart defects because of changes in their genes or chromosomes.  A combination of environmental exposures and genetic factors are likely responsible, but little is known about the specific cause.

How is it diagnosed?

Doctors sometimes hear a heart murmur (an odd, whooshing sound heard via stethoscope) due to the turbulence of blood flow through the narrowed area, after which, further tests might reveal subaortic stenosis.

When the narrowing is severe, symptoms such as lethargy, lack of appetite and difficulty breathing may signal an obstruction in infants. Rarely, fainting or chest pain also may occur.

The following tests may be utilized to find more details:

  • An electrocardiogram (EKG or ECG) can check the heart’s electrical action to reveal enlargement of chambers.
  • Chest X-rays create images of the heart and lungs and can show structural changes.
  • Pulse oximetry, a small gadget placed painlessly on a finger, is used to measure oxygen level of the blood.
  • An echocardiogram (ECHO) uses sound waves (ultrasound) to produce images of the heart and vessels on a screen. That reveals information about structure and function of the heart.
  • A cardiac MRI (magnetic resonance imaging) uses radio waves, magnets and a computer to form three-dimensional images of the heart, which can reveal structural abnormalities.
  • Cardiac catheterization involves insertion of thin, long tubes (catheters) through blood vessels and guided into the heart to obtain further information and is sometimes performed to treat some cardiac defects without surgery.

How is it treated?

Surgery is usually done through a vertical incision in the middle of the chest. Repair requires open heart surgery; that is, the patient is -placed on the heart-lung machine.

The subaortic stenosis is repaired by opening the aorta just above the aortic valve. The subaortic membrane can be seen through the valve. The membrane can then be cut out, leaving the left ventricle's outflow tract open and smooth.  This operation is called a subaortic resection.

It is uncommon to have major complications after a subaortic resection. It is possible to have a leftover membrane, though it is extremely unusual for that to cause any remaining obstruction. Other very uncommon complications include damage to the aortic valve itself, heart block (which is a problem with the electrical conduction of the heart), or creating a hole between the two pumping chambers (ventricular septal defect). Most patients who undergo a subaortic resection are able to be discharged with 3-4 days after surgery.

What are the long-term effects?

Surgery for subaortic stenosis typically has a high degree of success, and full recovery is usually expected unless there are initial complications. Subaortic stenosis may return a few years after effective surgery.

What follow-up care is needed?

Children should have regular checkups with their pediatric cardiologist. Doctors may prescribe antibiotics before any dental or other surgery.

Why choose the Children’s Heart Center?

As part of the Children’s Heart Center at Children’s Memorial Hermann Hospital, the affiliated cardiologists and affiliated cardiovascular surgeons collaborate as a multidisciplinary team to treat babies prior to birth, infants, children and young adults with congenital and acquired heart disorders.  The team of affiliated physicians, nurses and coordinators work together with you to determine the best treatment plan for your child.  Your child’s referring physician is also kept fully informed of your child’s treatment plan. 

At Children’s Memorial Hermann Hospital, the affiliated cardiologists and affiliated cardiovascular surgeons understand the unique challenges, circumstances and intricacies of caring for young patients with heart conditions. In addition to the team’s medical expertise, Children’s Memorial Hermann Hospital provides families with patient-centered care, keeping families fully involved as part of the child’s treatment team as well as offering resources to meet the needs of your entire family.

Contacts

Pediatric Cardiology Clinic
The University of Texas Health Science Center Professional Building
6410 Fannin, Suite 370
Houston, TX 77030
Phone: (832) 325-6516

Pediatric Cardiovascular Surgery Clinic
The University of Texas Health Science Center Professional Building
6410 Fannin, Suite 950
Houston, TX 77030

Clinic Phone: (832) 325-7234
Nurse Line: (713) 500-7324

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Note: This page is meant to be a helpful, informative introduction on the subject of subaortic stenosis in children. The information may not be applicable to all cases, especially if there are additional defects. It is not meant to replace the opinion of a personal physician.

03/2016 – This page was updated and approved by an affiliated pediatric physician at the Children’s Heart Center.